Rapid development in digital technology also affects a broadcasting field, and it stimulates the combination between a broadcasting network and the Internet. However, the conventional terrestrial television (TV) broadcasting method of the Advanced Television System Committee (ATSC) has a problem that the broadcasting cannot be received in mobile and portable terminals and even if it is received, the reception performance is poor. Detailed description on the ATSC DTV standards and the A/53 is presented at http://www.atsc.org.
FIG. 1 is a block diagram showing a conventional digital television (DTV) transmitting block. As illustrated in the drawing, data inputted into the transmitting block 100 are serial data streams each of which includes 188-byte MPEG-compatible data packets including a synch byte and 187-byte payload data. The inputted data are randomized in a data randomizer 101, and each packet is encoded to include 20-byte parity information for Forward Error Correction (FEC), Reed Solomon (RS) coding, and 1/6 data field interleaving, and 2/3 trellis coding. According to the Advanced Television System Committee (ATSC), the data randomizer 101 performs XOR on all payload data bytes inputted to a pseudo random binary sequence (PRBS) having the maximum length of 16 bits, which is initialized at the starting point of a data field.
The RS encoder 103 receives the randomized data and generates data of a total of 207 bytes per data segment by adding 20 RS parity bytes for FEC to the 187-byte data.
Among the inputted packet data, the randomization and FEC are not performed onto sync data which correspond to a segment sync signal.
Subsequently, data packets included in sequential segments of each data field are interleaved in a data interleaver 105, and the interleaved data packets are interleaved again and encoded in a trellis encoder 107. The trellis encoder 107 generates a stream of a data symbol expressed in three bits by using additional two bits inputted thereto. One bit of the inputted two bits is pre-coded and the other bit goes through a 4-state trellis encoding to be reduced into two bits. The outputted three bits are mapped to an 8-level symbol. The trellis encoder 107 includes 12 parallel trellis encoders and some pre-coders to generate 12 interleaved and encoded data sequences.
An 8-level symbols is combined with a segment sync and field sync bit sequences 117 which are transmitted from a synchronization unit (not shown) to thereby generate data frames for transmission. Subsequently, a pilot signal is added in a pilot adder 111. A symbol stream goes through Vestigial Side Band (VSB) suppressed-carrier modulation in a VSB modulator 113. An 8-level symbol stream of a baseband is finally transformed into a radio frequency signal in a Radio Frequency (RF) signal converter 115.
Error correction codes of the ATSC digital terrestrial TV broadcasting use RS codes as external codes and use concatenated codes formed of 2/3 trellis codes as internal codes.
FIG. 2 is a block diagram describing a structure of the trellis encoder of FIG. 1. The FIG. 2 shows a structure of the trellis encoder used in an internal error correcting encoder of the ATSC digital terrestrial TV broadcasting and it shows 8-VSB modulation symbol allocation based on the output of the trellis encoder.
Referring to FIG. 2, the trellis encoder 107 includes a pre-coding block and a 2/3 trellis encoding block. Two bits X1 and X2 from the data interleaver 105 are inputted into the trellis encoding block whose encoding rate is 2/3 to thereby produce three output bits z0, z1 and z2. The output bits z0, z1 and z2 are allocated with 8 symbols and they go through 8-VSB modulation in the VSB modulator 113. The number of memories of the trellis encoder 107 is two and thus, the number of trellis states becomes 4 during decoding.
However, conventional 8-VSB transceivers provide distorted signals in indoor and mobile channel environments due to variable channel and multipath phenomenon and, for this reason, signal reception performance is poor in receivers. To solve the problem, researchers are studying to develop an advanced transmission scheme having a strong error correction function, and it is called for to develop an excellent error correcting encoder suitable for the advanced transmission scheme, and an encoding method thereof.